Transmissible spongiform encephalopathies are incurable, fatal neurodegenerative diseases characterized by the accumulation of abnormal prion protein (PrPsc), neuronal cell death and vacuolation of brain tissue (1). The PrPsc protein is extractable from diseased tissue and is distinguished from endogenous PrPc by partial protease resistance and detergent insolubility (2). The transmissible agent is the PrPsc protein and it serves as a template for the molecular conversion of endogenous host PrPc into the abnormal PrPsc structural isoform (3, 4). Host expression of PrPc is necessary for disease transmission, as ablation of the PrPc gene prevents disease (5) whereas the over expression of PrPc followed by PrPsc challenge accelerates disease (6, 7). The molecular events that mediate neuronal PrPc to PrPsc conversion, not simply accumulated PrPsc, appears to be the initiating factor mitigating the neurodegenerative disease process (8, 9). Bovine Spongiform Encephalopathy (BSE) is one example of many prion diseases that include Scrapie in sheep and goats, chronic wasting disease (CWD) in deer and elk, and Kuru and Creutzfeldt-Jakob disease (CJD) in humans. Prions are thought to propagate in infected hosts by a novel mechanism that occurs when normal prion protein (PrPc) becomes “misfolded” into an abnormal infectious form (PrPsc), in a template-driven process. Unlike conventional microbes, prions do not require an agent-specific nucleic acid in order to multiply. The protein nature of prions makes them difficult to detect and nearly impossible to treat and control.
Current technologies inadequately address the inherent problems in prevention of PrPsc transmission, early detection and decontamination from animals and environmental by-products. Fundamentally, these issues reflect the fact that both PrPc and PrPsc have identical primary structures, differing in three-dimensional configuration only. To date no unique antibodies or surrogate markers have been identified that can distinguish between PrPc and PrPsc. This has created an extremely difficult and challenging dilemma in regard to the detection, vaccination and treatment of PrPsc (5).
Definitive diagnosis of PrPsc in animals requires assessment of clinical symptoms and post-mortem evaluation of brain tissue for spongiform degeneration. Pre-clinical assessment of animal status via non-invasive sampling has proven difficult and unreliable. The most definitive method to confirm the presence of infectious PrPsc requires an arduous animal bioassay. Biochemical assays all utilize a complex sequence of steps applied to tissue samples that exploit the resistance of PrPsc, relative to PrPc, to enzymatic degradation by Proteinase K (PK). Confirmation of PrPsc is defined by the detection of remaining PK resistance protein by a PrPc antibody (5-6). These methods detect only PK-resistant PrPsc, are prone to variability, and are inadequate for detection of low level PrPsc in contaminated samples such as blood.